The present invention relates to signal devices for pneumatic tires, and especially aims to provide a novel and improved device, which is adapted to be mounted onto an ordinary valve body of the tire filling valve, for producing an audible signal when the tire becomes deflated a certain amount, thereby warning the driver, in order that the tire can be inflated, replaced or repaired, to prevent running on a flat or under-inflated tire and thus avoid the injury to tires due to too little air therein.
As well known, air leakage of tires frequently occurs in running vehicles when a tire is pierced by nails or when something is wrong with its inner tube or air filling valve means. In case the leakage of air does occur and the driver is not aware of it and drives his vehicle in such deflated condition, then even over a short distance, the tire will be greatly damaged. This condition is even more serious when a leakage occurs in one of the two tires of the rear wheels, especially heavy duty vehicles such as trucks or buses, and thus the other tires will eventually be subjected to an excessive load which may develop and explosion.
Before the condition progresses to a serious stage the leaky tire should be inflated or replaced by a spare one, hence some means available for warning the driver in advance of the dangerous condition of the tire should be provided.
As is well known in the art to which this invention relates, many devices have been proposed to warn the operator of a vehicle when a tire pressure has decreased below a predetermined amount. However, difficulties have been encountered with such devices due to the fact that they require complicated structure and high cost to manufacture.